Girls only please! Help with spaghetti strap top?

Whenever I buy a cami top or spaghetti strap shirt with a built in bra, it always seems to reveal too much when I bend down. Why is this? Does this mean I'm bigger busted? I wish I could get one with a built in bra so that my bra straps don't show, but I can never find one that covers my bust when I bend down. Anybody else have this problem?